A new report from energy market analysis provider Montel EnAppSys, Curtailed Renewables in GB and Ireland, has revealed that over 12 Terawatt hours (TWh) of clean electricity was turned off across Great Britain and Ireland in 2025 due to grid constraints. This could have met the combined electricity demand of every domestic household in London for the entire year.
Key statistics from the report:
* 12.3TWh of renewable energy was curtailed across Great Britain and the island of Ireland in 2025.
* Just over 10TWh (10.2TWh) of this was curtailed in GB in 2025, a 22% increase in the amount of renewable power curtailed compared to 2024.
* Generators in Scotland alone accounted for over 98% of GB’s curtailed volume, curtailing just over 10TWh.
* Generators in Northern Scotland accounted for 8.8TWh of the overall curtailed volume. This in itself could have powered every domestic household in Scotland for the year.
* Ireland curtailed 2.1TWh, enough to power all homes in County Dublin for the year.
* 24% of all available wind energy was curtailed in Northern Ireland during 2025.
* Solar curtailment in the Republic of Ireland this year was more than four times higher than in 2024.
The report uncovers a growing disconnect between renewable generation and grid infrastructure capacity, something which has the potential to raise costs on consumer bills for years to come. This is primarily due to constraints and bottlenecks on the transmission network, which make it hard for power generated in certain areas (most notably North Scotland) to be transferred to areas where power is required for consumption.
Explaining the findings, report author and Senior Energy Market Analyst at Montel EnAppSys, Fintan Devenney said, “The analysis shows that only 61% of the wind power which could have been generated in Northern Scotland actually made it to the grid. Whilst the government’s goal of meeting 95% of annual demand with electricity generated from renewable sources by 2030 is laudable, ensuring the efficient siting and production of power to meet demand will become increasingly important.
“This is brought into sharper focus by the expected increase in electricity demand from new data centres wishing to connect to the grid as soon as possible, as well as the continued electrification of heating, transport and other sectors.
“It’s also worth noting that the amount of electricity curtailed in GB could have powered every data centre in the country in 2025. A recent policy paper suggested that data centres choosing to site themselves in Scotland could receive, in effect, an energy price discount of up to £24/MWh. This is an interesting method of incentivising the optimal siting of demand to solve these issues, particularly as the paper also suggests there will be no knock-on effect to bill-payers.”
The report also outlines the increasing impact of solar generation when it comes to curtailment, with the Republic of Ireland seeing solar curtailment rates for 2025 four times higher than in 2024.
Assessing the potential impacts of further curtailment as new renewables continue to connect to the grid, Devenney added: “A holistic view of policy which will enable the optimal siting of generation, sufficient investment in grid infrastructure and the correct investment signals to help alleviate grid constraints is now crucial and the Strategic Spatial Energy Plan (SSEP) will be key to achieving these aims.”
